Radio receiving circuit



y 21, 2 A. J. FORBES. 1. 1

RADIO RECEIVING CIRCUIT Filed Dec. 10, 192;

iumvmn ALEXANDER J. FORBES Patented May 21, 1929.

' UNITED STATES ALEXANDER FORBES, OF OAKLAND, CALIFORNIA.

RADIO RECEIVING CIRCUIT.

Application filed December 10, 1924. Serial No. 754,990. 7

My invention relates to circuits for radio reception, and is particularly adapted for receiving signals transmitted on either short or long wave lengths with a crystal detector.

A further object of the invention is to provide a receiving circuit consisting essentially of a tuned antenna circuit having a plurality of inductances and condensers in series, an untuned secondary conductively coupled thereto, and a rejector loop circuit conductively coupled to said secondary circuit.

The figure on the drawing is a schematic diagram of connections of the preferred e1nbodiment of the invention.

The tuned antenna circuit consists of an inductance 5 of substantially 40 turns connected in series with an inductance 6 of substantially 12 turns and both forming an in ductance 4. The lead-in from the antenna 1 is connected to the switch arm of a two point switch 2, one point of which is connected by a conductor 3 to one end of the inductance 5, the other switch point being connected by a conductor 25 to the junction 26 connecting inductances 5 and 6. For the reception of long wave lengths the .inductances 5 and 6 are connected in the antenna loop circuit and for the reception of short wave lengths theinductance 6 only is in circuit when the switch 2 is moved to the lower point shown in the diagram. 'A secondinductance 8 is close coupled with the inductance 4 and comprises coils 9 and 10in seriesand joined at 24. The other terminal of coil 9 is connected to the coil 6 by a conductor 7 which places all of the above mentioned coils in series.

An untuned secondary comprising the head phones 21 shunted by a fixed condenser 22 and in series with a crystal detector 20 is conductively coupled to the tuned antenna circuit by the conductors 23 and 18 at the j unction points 24 and 19.

A rej ector loop circuit comprising a fixed inductance 14 and a variable condenser 13 in series is conductively coupled to the junction point 19. A ground lead 15 is tapped ofi the first turn 16 ofthe coil 14 and is connected through a variable condenser 17 to ground.

The inductance 14 of the rejector circuit is positioned substantially at right angles to the inductances 4 and 10 in order to increase the selectivity of the set.

WVhen it is desired to receive signals on long wave lengths the switch 2 is connected to the lead 25 and for short wave length reception the switch is connected to the lead 3. lVith either connection the secondary circuit is tuned to resonance by adjusting the capacity of the variable condensers 13 and 17.

My invention may be considerably modified to suit various circumstances in thatthe inductances may be altered and the relative closeness of the coupling changed. However,

. I have found the circuit satisfactory with the inductances above described and using variable condensers of suitable capacity and located as shown.

Having described my invention, I claim 1. A radio recelving circuit comprising a tuned antenna circuit consisting of an antenna, a two-point switch and two pair of fixed inductances connected in series, each pair of inductances being inductively coupled, said switch being adapted to disconnect one of the inductances in the first pair, an untuned secondary circuit comprising a pair of head phones and a crystal detector in series and connected in parallel with one of the inductances in the said second pair of fixed inductances, and a rejector loop circuit including a pair of variable condensers and conductively connected between the untuned secondary circuit and ground.

2. A radio receiving circuit comprising an antenna a main inductance in two sections in circuit therewith, having the first section of about three times the inductance of the second section, a second inductance in two sections in circuit with the main inductance, and inductively coupled thereto, having a first section of about one quarter the inductance of its second section, a lead from the end of the second inductance to a circuit having a fixed .of the second inductance.

In testimony whereof I afiix my signature.

ALEXANDER J. FORBES. 

